Phytochemical profiles and protein glycation inhibitory activities of three oak species

The Quercus genus (oaks) comprises valuable plant resources that are used in many fields, including cosmetics, foods, and pharmaceuticals. Nonetheless, overall chemical profiling and anti-glycation component identification have not been thoroughly performed. In the present study, 70 % ethanolic and water extracts from three oak species (Quercus dentata, Q. serrata, and Q. aliena) showed antioxidant and anti-glycation potential. Thus, the components of the three oak species were profiled using ultra-performance liquid chromatography coupled with electrospray ionization and quadrupole time-of-flight mass spectrometry. The analysis showed that phenolic acids, ellagitannins, ellagic acid, procyanidin, and flavonoid (quercetin, myricetin, kaempferol, isorhamnetin, and taxifolin) glycosides are the main phenolic compounds. Based on the fluorescence assay, they act as strong inhibitors of non-enzymatic advanced glycation end-products (AGEs) formation in the bovine serum albumin (BSA) and skin proteins (collagen and elastin). Furthermore, mass fragmentation analysis demonstrated that ellagitannin, procyanidin B1 and flavonoid glycosides effectively trapped methylglyoxal (MGO), a reactive carbonyl intermediate and an important precursor of AGEs, to generate mono-, di-, or tri-MGO. Collectively, ellagic acid, ellagitannins, procyanidin B1, and flavonoid glycosides, the main active ingredients of three oak species (Q. dentata, Q. serrata, and Q. aliena), may be employed as lead structures in the development of functional foods or drugs to prevent diseases caused by aging and excessive sugar consumption.